Magnetic fibrous products which must be prevented from being counterfeited and which are provided with a genuineness checking function have been proposed.
For example, Patent Document 1 proposes a magnetic cellulose material, in which a metal oxide mainly containing magnetic iron is deposited in a cellulose material, obtained by immersing a cellulose material in a metal salt solution, adjusting the pH and temperature of the solution, and subjecting the solution to a heat treatment or the like. However, the magnetic cellulose material obtained by this method has inferior magnetic properties due to small magnetic material content. Moreover, since the magnetic material adheres to the vicinity of the fiber surface, the paper strength is decreased.
Patent Document 2 proposes counterfeit prevention paper obtained by preparing a magnetic polymer element by mixing magnetic metal powder into a synthetic resin solution and jetting the resulting solution into a coagulating solution from a nozzle, cutting the magnetic polymer element to a length of about 2 to 10 mm, and forming the magnetic polymer elements into paper together with pulp fibers. However, since the magnetized fiber described in this document requires a complicated manufacturing apparatus, it is disadvantageous from the viewpoint of manufacturing cost when manufacturing the magnetized fibers in a small lot. Moreover, since the resulting magnetized fibers have inferior self-adhesion, the magnetized fibers are easily removed from the paper.
Patent Document 3 proposes counterfeit prevention paper containing a magnetic fibrous product obtained by causing magnetic particles with an average particle size of 0.1 to 100 μm to adhere to the surface of a fibrous product with a weight average fiber length of 5 mm or less using a dry impact blending method. However, since the magnetic material adheres to the vicinity of the fiber surface, the counterfeit prevention paper obtained by this method decreases the paper strength.
Patent Document 4 and Non-Patent Documents 1 to 4 disclose magnetized fibers containing a magnetic material in the fiber inner cavity and methods of manufacturing the magnetized fibers in relation to the present invention.    [Patent Document 1] Japanese Patent Publication No. 4-12738    [Patent Document 2] Japanese Patent Application Laid-open No. 7-214955    [Patent Document 3] Japanese Patent Application Laid-open No. 11-107161    [Patent Document 4] Japanese Patent Application Laid-open No. 6-93564    [Non-Patent Document 1] Japan Tappi Journal, vol. 57, (3), p. 106, 2003    [Non-Patent Document 2] Japan Tappi Journal, vol. 57, (4), p. 90, 2003    [Non-Patent Document 3] Japan Tappi Journal, vol. 57, (5), p. 112, 2003    [Non-Patent Document 4] Japan Tappi Journal, vol. 57, (7), p. 112, 2003
The present invention has been achieved in view of the above-described conventional technologies. An object of the present invention is to provide identification functional paper which allows secure measurement of a change in signal caused by a magnetic material and excels in waveform reproducibility when measuring a single specimen two or more times, and an identification card comprising the identification functional paper.